Tham has been co-chairman and regional executive creative director for Ogilvy & Mather Asia Pacific since 1999.
During that period, the agency has been consistently recognised as one of the most creative networks in the Asian region, winning 北京赛车pk10 Brief Asia's creative network of the year for seven consecutive years.
Tham, a Singaporean, will divide his time from the beginning of next year between New York and the rest of the world. He will continue to have a supervisory role over Asia.
Shelly Lazarus, chairman and CEO of Ogilvy & Mather Worldwide, said: "Khai's record speaks for itself. He gets results. He believes in great work that works. And above all, he is an Ogilvy 'gentleman with brains' to his bones."
Tham said: "I'm honoured to take on this worldwide role. I believe opportunities abound in these frightening yet very exciting times.
"The marvellous thing is that I shall continue to work with Miles Young who will be taking on the new global CEO role in January. We've been a team in Asia for a long time, and we both reckon that renewing our partnership will make for some spectacular success on the bigger stage."